1. Field of the Invention
The present invention relates to an injection pump control system for a distribution type fuel injection pump in which the rotation of a rotor causes plungers radially arranged therein to be oppositely reciprocately moved by the inner cams of cam rings arranged on the outer side of the rotor whereby fuel is introduced into and pressurized in pump chambers and then is successively distributed and delivered through a distribution mechanism to the respective cylinders of an engine. The control system comprises a plurality of electromagnetic valves each disposed in the fuel passage to each pump chamber, and the duration of opening of the electromagnetic valves is controlled by an electric control circuit to control the amount of fuel delivered.
2. Description of the Prior Art
In a known system of this type in which an electromagnetic valve is positioned in each fuel inlet passage whereby the amount of fuel drawn in during each suction stroke of the fuel pump is controlled in accordance with the duration of opening of the electromagnetic valve to thereby accomplish the fuel metering, the number of operations of the electromagnetic valves becomes equal to the number of fuel delivery operations (equal to the number of suction operations) of the fuel pump with the result that at high engine speeds the number of operations of the electromagnetic valve per unit time increases with increase in the number of cylinders and the operating cycle inevitably decreases. In the case of a four cycle engine having six cylinders and the maximum rotational speed of 3600 rpm, the operating cycle of the injection pump becomes 5.5 msec and consequently the possible maximum metering time of the electromagnetic valves becomes 5.5 msec. On the other hand, the operation of the electromagnetic valves involves a delay time of the order of 1.5 msec per driving timing pulse voltage, and consequently if this delay time becomes not negligibly great in relation to the operating cycle of the injection pump, this results in a deteriorated metering accuracy.